Taylor Swift at Wembley Stadium: "Niall Horan is here!!"

Niall Horan joined Taylor Swift on stage at Wembley Stadium last night (June 22) as part of Swift's reputation Tour.

Swift brought out the "Flicker" star as a huge surprise for an ecstatic audience. This is how she introduced him: 'I wonder if a crowd this incredible might be up for a surprise performance. Would you, you think?

'So, ya know they say, when you're starting out something new, learn from somebody's who's done it before, learn from a pro.

'So I called up somebody who has played Wembley Stadium bunches of times. Would you be excited if I told you Niall Horan is here!'

The duo performed Horan's hit "Slow Hands" which they soundchecked earlier that day.

The 72,000 capacity venue will see Swift perform a second night tonight with her support acts Charli XCX and Camila Cabello.